Award Ceremony Speech

The Royal Swedish Academy of Sciences has decided to award this
year's Nobel Prize in Physics jointly to Dr Leon Lederman, Dr
Melvin Schwartz and Dr Jack Steinberger. The citation has the
following wording, "for the neutrino beam method and the
demonstration of the doublet structure of the leptons through the
discovery of the muon neutrino".

The neutrino figures in George Gamow's
entertaining book "Mr Tompkins Explores the Atom", written in the
1940's. Gamow describes how Mr Tompkins in a dream visits a
woodcarvers shop, where the building blocks of the elements -
protons, neutrons and electrons - are stored in separate caskets.
Mr Tompkins sees many unusual things, but above all a carefully
closed, but apparently empty casket labelled: "NEUTRINOS, Handle
with care and don't let out". The woodcarver does not know
whether there is anything inside. The friend, who had presented
the casket to him, must have been Wolfgang Pauli, Nobel
Laureate in Physics in 1945, who proposed the existence of the
neutrino in the early 1930's.

The neutrino is electrically neutral and
almost or totally massless - hence the name. It cannot be seen
and it interacts only weakly with atoms. It travels with the
speed of light or nearly so. It is impossible to completely stop
a beam of neutrinos. To do so would require a wall of several
hundred thousands of steel blocks stacked in depth one after the
other, each with a thickness corresponding to the distance from
here to the sun.

Our sun is a source of neutrinos, which are
copiously produced in its hot central region. They pass through
the whole sun without much difficulty. Every square centimeter on
Earth is bombarded by many billion solar neutrinos every second
and they pass straight through the Earth without leaving a
noticeable mark. The neutrinos are - if I may say so - "lazy",
they do almost nothing but steal energy, which they carry
away.

The great achievement of the Nobel prize
winners was to put the "lazy" neutrinos to work. Lederman,
Schwartz and Steinberger are famous for several other important
discoveries concerning elementary particles. At the time of the
neutrino experiment they were associated with Columbia University
in New York. They and their co-workers designed the world's first
beam of neutrinos at the Brookhaven National Laboratory, using
its large proton accelerator as a source. Their neutrinos had
considerably more energy than usual, because they were produced
from the decay in flight of fast moving mesons. Such neutrinos
are much more apt to interact with matter and the collisions with
atomic particles become much more interesting. Although a
neutrino collision is a rare event it can be spectacular at high
energy - and very informative.

In their pioneering experiment the
prizewinners dealt with a total of about 1014, i.e. a
hundred thousand billion neutrinos. To catch just a few dozen
collisions from all these, the research team invented and built a
huge, sophisticated detector with the weight of 10 tons. Other
unwanted particles in the beam had to be prevented from entering
the detector. An enormous 13-meter thick steel wall served this
purpose. To save time and money, the wall material was taken from
scrapped battleships. Unwanted particles came also from the
outside in the form of cosmic ray muons. Various tricks were used
to prevent these muons from playing a role as false neutrinos.
The first neutrino beam experiment was a bold endeavor, which
proved successful. The method has since been much used as a tool
for investigating the weak force and the quark structure of
matter. It has also been used to investigate the neutrino
itself.

At the time of the prizewinners'
experiment, physicists were puzzled by the fact that a possible,
alternative decay of the muon particle did not happen. No known
law forbade it, and there is a general principle which says that
a process must occur unless it is explicitly forbidden by law.
The mystery was solved when the prizewinners' team discovered
that Mother Nature provides two completely different species of
neutrino, as had been suggested by a theoretical analysis. The
old type of neutrino is paired with and may be transformed into
an electron, the newly discovered type of neutrino is similarly
paired with the muon. The two pairs constitute two separate
lepton families, which never mix with each other. Thus, a new law
of Nature had been discovered.

Cosmologists and physicists alike want to
know how many different lepton families, i.e. how many neutrino
species there are in Nature. Present ideas about the birth and
early evolution of our universe cannot tolerate more than four. A
third is already on the books. One of the goals of the
experimental program at the large LEP accelerator ring at CERN,
which will be ready to start operation next summer, is to give a
precise answer as to the number of neutrino species and thus the
exact number of lepton families in the universe.

Professors Dr Lederman, Dr Schwartz and Dr
Steinberger,

You started a bold new line of research, which gave rich fruit
from the beginning by establishing the existence of a second
neutrino. Furthermore, problems which could not even be
formulated at the time of your experiment, have been successfully
elucidated in later experiments using your method. The pairing of
the leptons, which you discovered, is also of much wider
applicability than could be foreseen at the time and is now an
indispensible ingredient in the standard model for quarks and
leptons.

On behalf of the Royal Swedish Academy of
Sciences, I have the privilege and the great honour to extend to
you our warmest congratulations. May I now ask you to receive the
1988 Nobel Prize in physics from the hands of His Majesty the
King.